This at once places the group above the mere temporary aggregations, such as the crowd or the mob. The ethnic group is formed by the thoughts and aims of the lives of its members, not by their ephemeral emotions and actions. Compared with nation, stock, or race, it is a generic term; for by “nation” we understand all united in the acceptance of one form of government; by “stock,” those speaking dialects or tongues derived from one primitive language (linguistic stocks); and by “race,” those connected by identity of physical traits. The “tribe” is merely the primitive form of the nation, while in English “folk” has a current application to certain classes in society and not to the whole of it. The correlative of the ethnic group, or, in these pages, “the group,” in German is _Volk_ and in French, _le peuple_. How these ethnic groups are formed, under what complex conditions their differences arise, what influences are the most potent in their creation and preservation, will be considered in detail hereafter. At present it is sufficient to mention certain general principles, applicable to the formation of all ethnic groups. First, it must be borne in mind that mere similarity and geographical contiguity are not enough to constitute an _ethnos_. The Fuegian hordes live under the same sky, speak closely related dialects and are physically alike; but no one would pretend that there is any unity among them. Their roving bands never meet but to fight and their only social occupation is mutual destruction. Nor would there be any true unity in a society however peaceful where each family isolates itself to the utmost from its neighbours and seeks to limit all its efforts and sympathies to its own members. Such a society might become high in numbers and extended in area; but it would have no true unity. It might even develop considerable results in thoughts, study, and invention; but they would remain sterile to the general weal, and contribute little or nothing to the progress of the race. Such was the condition of parts of Europe in the feudal ages. The ethnic life is a mental life, and this consists not in the sameness brought about by the environment, nor even in ideas and acquirements, but in movement, comparison, and association of ideas. The unity not merely of present traits but of future aims, not merely of ideas but of ideals, is the true unity which constitutes the ethnic mind. This is the foundation fact which must be constantly present to the student, if his researches in ethnic psychology are to be profitable. In this it differs from racial psychology, for while doubtless each race has mental advantages and deficiencies which are its own and which largely decide the destiny of its members, these are not united in pursuit of one end. There is no unity of will and purpose.